As a prior art, there is a so-called bidirectional converter; however, performing a feedback control by connecting a plurality of converters with each other and by using a common DC bus voltage means that a plurality of voltage feedbacks operate in parallel within a single control system. This causes interference between mutual controls, whereby the control has not been successful.
For example, a bidirectional converter A and a bidirectional converter B are connected in parallel, and a connected part thereof is referred to as a common DC bus. Here, in a case where the bidirectional converter A is regarded as an input side and the bidirectional converter B is regarded as an output side (called a mode A to B), electricity is supplied from an input side of the bidirectional converter A, then the electricity is output to the common DC bus, then the electricity is supplied to an input side of the bidirectional converter B, and finally, the electricity is output to an output side of the bidirectional converter B.
Furthermore, in a case where an output from the bidirectional converter B, which occurs first, is regarded as an input and an input into the bidirectional converter A is regarded as an output (called a mode B to A) in an operating mode, electricity is supplied from the input side of the bidirectional converter B, then the electricity is output to the common DC bus, then the electricity is supplied to the input side of the bidirectional converter A, and finally, the electricity is output to an output side of the bidirectional converter A.
A concept of a main circuit in this manner has been in existence, and operation by switching input and output feedbacks between the mode A to B and the mode B to A has been possible. Note that as a literature related to such background art, Non Patent Literature 1 below, for example, may be listed.